Most countries have an independent judiciary; a system of courts which hears and decides criminal and civil cases. The conduct of the courts is defined by constitutions, legislation, government regulations and precedents set by previous court decisions. These guidelines cover such areas as judicial authority, jury selection, interrogation methods and rules of evidence. Evidence guidelines are those laws and restrictions which determine the methods that can be used to gather evidence, the way evidence must be handled during the course of an investigation and trial, and the types of evidence which will be considered admissible in court.
For English-speaking countries such as Australia, Canada and the United States, the foundation for evidence guidelines can be found in English common law. The Magna Carta, signed by King John in 1215, was the beginning of written guidelines for regulating what evidence would be admissible in a court. Prior to this time, a person could be tortured, submitted to a trail by ordeal or merely arrested on a rumor or whim. The Magna Carta mandated that evidence against a person could not be obtained by torture.
Over time Parliament and the courts developed more guidelines to protect the accused and to help assure that the evidence introduced was valid. After the Revolutionary War, the United States included several judicial and evidence guidelines to protect the rights of citizens in its Constitution. According to the Fourth Amendment, government authorities are not allowed to search a person or his property without a warrant from a judge and such a warrant can only be issued upon a showing of probable cause that the person may be guilty of a crime. Evidence seized without following this procedure is not allowed.
The Constitution also outlawed the use of anonymous testimony as evidence in a criminal court, insisting that the accused has the right to face and question his accuser. The Fifth Amendment to the Constitution states that the accused could not be forced to testify against his will, that he has the right to know what charges he faces, and the right to have an attorney represent him. Unfortunately, not everyone is aware of his rights, so the opportunity exists for law enforcement officers to take advantage of a person’s ignorance during an interrogation. To assure that these evidence guidelines were followed, the United States Supreme Court ruled in Miranda vs. Arizona that law enforcement officials are required to inform a person of his rights against self-incrimination and for legal representation prior to questioning.
Other evidence guidelines adopted by many national and regional governments include restrictions on what can constitute admissible evidence. For example, most courts will not allow hearsay evidence, or testimony about which a witness has no personal knowledge. Such testimony is considered gossip or rumor. Rules are also in place defining how evidence is processed and stored to ensure that it does not become tainted or altered.
Evidence guidelines also strictly limit when testimony about the behavior of the victim or past criminal history of the accused can be admitted. In most cases, such testimony must first be shown to have a direct bearing on the case before it is allowed. In a rape case, it is not admissible to introduce the fact that the victim has had a sexual relationship in the past as evidence that she is therefore not a victim of any sexual attack. In the case of a person who is charged with rape, evidence guidelines will permit testimony regarding past convictions of similar sexual crimes, but not a past record for unrelated offenses such as burglary, theft or any other crime.